Effect of ration levels on food utilisation in the grasshopper Poecilocerus pictus

Abstract

Reduced rations of Calotropis gigantea produced a number of negative effects on the grasshopper Poecilocerus pictus such as heavy mortality (42% at 25% ration as aginst 11% at 100% ration), extension of hopper period (from 75 days about 113 days) and increase in the number of instars (from 6-7). At the tested 100, 50 and 25% ration levels, female hoppers attained a final body (dry) weight of 693, 320 and 208 mg; the corresponding values for the males were 439, 365 and 224 mg. Males receiving 100, 50 and 25% rations consumed 4238, 2641 and 1425 mg (dry) food at the rate of 127, 84 and 77 mg dry weight/g live insect/day; females receiving similar rations consumed 5165, 3558 and 1589 mg of food at the rate of 115, 84 and 73 mg/g/day. Hoppers reveiving different rations assimilated about 50% of the ingested food. Assimilation efficiency varied from about 45-56% as functions of sex and ration levels and averaged to 50%; these variations were not statistically significant. Conversion efficiency (K ₂) increased with decreasing ration levels from 29-37% in females and from 21-41% in males. Individuals receiving the lowest ration displayed reduced metabolic rate, which partly accounts for the increased rate and efficiency of conversion.